The role of home-made ice cream as a vehicle of Salmonella enteritidis phage type 4 infection from fresh shell eggs

A family outbreak of Salmonella enteritidis PT4 infection is described in which home-made ice cream was identified as the vehicle of infection. The ice cream contained approximately 10⁵ S. enteritidis PT4 organisms per gm and was probably contaminated by an infected shell egg containing between 10⁵−10⁸ organisms. The continued relevance of the Chief Medical Officer's warning on the use of raw shell eggs is highlighted. Home-made ice cream using the same recipe as ice cream that had been incriminated as the cause of the family outbreak of S. enteritidis PT4 infection was used to study the growth of the organism that might have occurred in the 3-4 h it took to prepare the product. When the inoculum was in the stationary phase, as it would be from shell or other cross contamination, there was a lag phase of 3 h before growth occurred at room temperature. Even when actively multiplying organisms were introduced, as may be found in an infected egg, there was less than 3 log₁₀ increase in the salmonella count in 4 h at room temperature. It was, therefore, given the high S. enteritidis count, unlikely that the ice cream was cross-contaminated. By contrast, raspberry sorbet at pH 3·73 proved to be lethal to a large inoculum of S. enteritidis and may be a relatively safe raw egg containing product.